Whenever a user attempts to communicate with another user electronically there is the possibility of being placed on hold. This could happen when the user is first trying to get in contact with the other user but is not able to be immediately connected and thus is put on hold while waiting for the other user to become available. It can also happen after the two users have already established their connection. For example, if one of the users is notified of an urgent task that needs immediate attention but has not yet finished his first call, he may put the other user on hold.
To address this, many systems use a camp-on feature which allows a user to have his phone connected to the called user when the called user completes his call. When the called user hangs up, the system rings and/or alerts the called user of the caller's call.